The Organic Light-Emitting Display (OLED) utilizes the phenomenon that the illumination due to the carrier injection and recombination under the electric field driving of organic semiconductor illuminating material. The illuminating principle is that the Indium Tin Oxide (ITO) transparent electrode and the metal electrode are respectively employed as the anode and the cathode of the Display. Under certain voltage driving, the Electron and the Hole are respectively rejected into the Electron and Hole Transporting Layers from the cathode and the anode. The Electron and the Hole respectively migrate from the Electron and Hole Transporting Layers to the Emitting layer and bump into each other in the Emitting layer to form an exciton to excite the emitting molecule. The latter can illuminate after the radiative relaxation.
The OLED possesses advantages of being thinner, lighter, active lighting (without a backlight source), no view angle concern, high resolution, high brightness, fast response, low power consumption, wide usage temperature range, strong anti-shock ability, low manufacture cost and possible flexible display.
The OLED can be categorized into two major types, which are the passive driving and the active driving, i.e. the direct addressing and the Thin Film Transistor (TFT) matrix addressing. The active driving is also called Active Matrix (AM) type. Each light-emitting element in the AMOLED is independently controlled by TFT addressing. The light-emitting element and the pixel structure comprising the TFT addressing circuit require the power supply signal line to load the direct current output voltage (OVDD) for driving.
However, in a large scale AMOLED display device, a certain resistance unavoidably exists for a backplate power supply signal line. The driving current for all the pixels are provided by the OVDD. The power supply voltage in the area close to the OVDD power supplying position is higher than the power supply voltage in the area away from the power supplying position. The phenomenon is named power supply voltage drop (IR Drop). Because the voltage and the current of the OVDD are related. The IR Drop can cause the current difference among different areas which the uneven brightness (mura) phenomenon can happen thereby as displaying.
For now, the compensation method of AMOLED has internal compensation and external compensation. The internal compensation of the AMOLED is to compensate the threshold voltage (Vth) of the TFT or the channel mobility (μ) but not the IR drop; the external compensation can be optical compensation and electrical compensation. The electrical compensation can merely compensate the threshold voltages of the driving TFT and the OLED but not the IR Drop. The optical compensation can compensate the IR Drop but the compensation in time cannot be achievable.